1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display having a quad type pixel structure including red, green, blue, and white subpixels and a method of driving the same.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a moving picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as display devices in portable devices, such as office equipment and computers, because of the thin profile of an active matrix type liquid crystal displays. Accordingly, cathode ray tubes (CRT) are being rapidly replaced by active matrix type liquid crystal displays.
As shown in FIG. 1, because a liquid crystal display switches a data voltage supplied to liquid crystal cells Clc using a thin film transistor TFT formed in each of the liquid crystal cells Clc to actively control data, the image quality of a moving picture can increase. In FIG. 1, a reference numeral Cst indicates a storage capacitor for keeping a charging voltage of the liquid crystal cell Clc at the data voltage, DL a data line to which the data voltage is supplied, and GL a scan line to which a scan voltage is supplied.
The liquid crystal display is driven in an inversion manner in which polarities of the neighboring liquid crystal cells Clc are opposite to each other and polarities of the neighboring liquid crystal cells Clc are inverted every 1 frame period, so as to reduce direct current (DC) offset components and to reduce the degradation of liquid crystals. In the inversion manner, if the data voltage with a predetermined polarity is dominantly supplied to the liquid crystal cell Clc for a long time, image sticking occurs in the liquid crystal display. In the invention, because the image sticking occurs by repeatedly charging the liquid crystal cells Clc to a voltage with the same polarity, the image sticking is called direct current (DC) image sticking. For example, in case the data voltage is supplied to the liquid crystal cells Clc in an interlaced manner, the DC image sticking occurs. In the interlaced manner, the data voltage is supplied to the liquid crystal cells of only odd-numbered horizontal lines during odd-numbered frame periods, and the data voltage is supplied to the liquid crystal cells of only even-numbered horizontal lines during even-numbered frame periods.
FIG. 2 is a waveform diagram showing an example of the data voltage supplied to the same liquid crystal cells Clc in an interlaced manner during 1st to 4th frame periods.
As shown in FIG. 2, a positive data voltage is supplied to the liquid crystal cells Clc during odd-numbered frame periods, and a negative data voltage is supplied to the liquid crystal cells Clc during even-numbered frame periods. In the interlaced manner, a high positive data voltage is supplied to the liquid crystal cells Clc of the odd-numbered horizontal lines during only the odd-numbered frame periods. Therefore, as can be seen from the waveform diagram in a box area of FIG. 2, because the positive data voltage is supplied more dominantly than the negative data voltage during 4 frame periods, the DC image sticking appears.
FIG. 3 illustrates an experimental result of DC image sticking resulting from interlaced data. If an original image shown at a left side of FIG. 3 is displayed on the liquid crystal display in the interlaced manner for a predetermined period of time, the data voltage supplied to the liquid crystal cells Clc changes as shown in FIG. 2. As a result, after the predetermined period of time elapsed, if the data voltage with a middle gray level, for example, the data voltage with 127-gray level is supplied to the liquid crystal cells Clc of the entire screen, the original image is dimly displayed like an image shown at a right side of FIG. 3. Namely, the DC image sticking appears.
As another example of the DC image sticking, as shown in FIG. 4, if the same image moves or is scrolled at a predetermined speed, voltages of the same polarity are repeatedly accumulated on the liquid crystal cells Clc depending on a relationship between the size and a scrolling speed (moving speed) of the scrolled image. Hence, the DC image sticking may appear. FIG. 4 illustrates an experimental result of the DC image sticking appearing when an image having an oblique line pattern and a character pattern moves at a predetermined speed.